Adam Ratner, director of pediatric infectious diseases at Hassenfeld Children’s Hospital at NYU Langone Health. “You definitely don’t want either infection, and you don’t want them together,” says Dr. Getting sick with the flu can therefore potentially make animals more vulnerable to getting infected with SARS-CoV-2.

This priming was unique to influenza, because it activates the same receptor, also found in people, that SARS-CoV-2 uses to enter and infect cells. They found that influenza can make it easier for SARS-CoV-2 to infect cells in the respiratory tract, including the lungs, of mice.

In another study involving mice, published in 2020, researchers from Wuhan University reported even more concerning data on how influenza and SARS-CoV-2 might interact. The co-infected animals also showed lower levels of virus-fighting antibodies and immune T cells against each virus, compared to mice infected with either influenza or SARS-CoV-2 alone.

In March, researchers in South Korea found that co-infected mice were sicker for a longer time than those with just one viral infection, and they also had higher levels of inflammation that contributed to pneumonia. “We can, with some confidence, say that being infected with flu and SARS-CoV-2 at the same time increases the risk of both needing to go on a ventilator and needing intensive care, and of death,” says Baillie.Īnimal studies also show that those who are co-infected with SARS-CoV-2 and influenza tend to do worse than those infected with either virus alone. In one 2021 study on COVID-19 co-infections, including 17 people who tested positive for both influenza and COVID-19 at King Fahad Hospital in Medina, Saudi Arabia, their rates of hospitalization and death were higher than those for people infected with COVID-19 a type of bacteria that can cause respiratory tract infections. The same could be true when flu and COVID-19 combine classic symptoms, including fever, chills, fatigue, and coughing, could become more intense for some people. Already, doctors know that people who get both the flu and a cold at the same time tend to be sicker than those who are only infected with one virus. But the limited early data-some from people, but mostly from animals-are not encouraging. Gates and others stress that there aren’t extensive data yet to be sure exactly what will happen when people are infected with both influenza and SARS-CoV-2. Khalilah Gates, a pulmonary critical care physician at Northwestern University. “Are two viruses that cause huge inflammatory responses together going to make that response worse? Theoretically, yes,” says Dr. That opens the possibility that people could get the two infections at the same time-which experts believe could be both unpleasant and dangerous. That could mean influenza will sweep through North America and Europe with equally aggressive force this winter, alongside rising cases of COVID-19. Already, the flu season in the southern hemisphere-which runs from April to October and serves as a harbinger of what’s to come for the U.S.-has been severe, with cases in Australia three times higher than average compared to the past five years. Health experts are warning that flu cases could rise again this winter, and that the combination of influenza and COVID-19 together could pose a real public-health threat that sends more people to the hospital and in need of intensive care. And once people began mingling more during the next flu seasons, widespread use of masks blocked influenza’s chances of infecting large numbers of people.īut that could change this flu season, as mask mandates have disappeared and more people are interacting in close quarters in school, workplaces, sports events, public transport, and more. During the first flu season during the pandemic, lockdowns kept people indoors and away from one another, limiting the virus’ ability to spread. So far, COVID-19 has come with one small silver lining for health: cases of influenza have dropped dramatically.

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